1. The Field of the Invention
The present invention relates to analyzing signals between a host and a device by tapping the bus. More particularly, embodiments of the invention relate to a tap for tapping a bus between a host and a device.
2. The Relevant Technology
Protocol analyzers are devices that detect, diagnose, and solve problems that occur on networks or over busses used by hosts and attached devices. Typically, protocol analyzers view traffic on the network, over a bus or over a connection as the traffic occurs. This enables the traffic to be monitored in real time in some instances. As the data or traffic is being monitored, the protocol analyzer may detect a problem or a defined condition. At this point, the analyzer triggers and captures the data present on the network or on the bus. The amount of data captured can depend on the size of the analyzer's buffer. The analyzer can also be configured such that the captured data represents data that occurred before the triggering event, after the triggering event, and/or both before and after the triggering event. In addition, data can also be captured without a triggering event. Rather, data can simply be captured until the buffer is full. In effect, the capture is a snapshot of the data that was present on the network or bus around the time that a problem occurred or a condition was detected or when a capture was initiated. The captured data can then be analyzed to help resolve many problems and improve communications in a network or between a host and a device.
Some protocols, however, are difficult to implement in analyzers. SD (Secure Digital Cards), SDIO (SD Input/Output Cards, MMC (Multimedia Cards) and CE-ATA (Consumer Electronics-Advanced Technology Attachment) are examples of protocols that are difficult to analyze.
Some of the reasons for the difficulty in implementing a protocol analyzer for these and other protocols are related to the physical sizes of devices that use SD, SDIO, MMC or CE-ATA. Other reasons are related to the cost. CE-ATA connectors, for example, have a limited number of insertion cycles. Because protocol analyzers are repeatedly connected and disconnected, cost can become a significant issue when analyzing CE-ATA. In addition, many consumer devices do not operate at the same voltage levels. This can complicate the issue of connecting a system to a protocol analyzer when the voltage levels are not known beforehand. When the bus is electrical in nature rather than optical, there are also issues related to impedance matching and capacitive loading.